Conversion of hydrocarbon oils



Feb. 10, 1942.

GASES &

LOW-END POINT c. G. GERHOLD 2,272,297

CONVERSION OF HYDROCARBON OILS Filed July 14, 1939 CASES 8- HIGH ENDPOINT GASOLINE VAPORS GASOLINE VAPORS 2* 2* No as SEPARATING a CONDENsmc SEPARATING a. FRACTIONATING zo NE) i-RAcT|oNATmc ZONE 6 ZONE FULLBOILING RANGE CRACKING 7 GASOL'NE CRACKING ZONE 8 I" 22 ZONE 3 I6 HEAVY42 23-. LIGHT A RESIDUAL RESIDUAL LIQUID (l3 ['4 J5 LIQUID FIRST] 1 26251 2 RECYCLE-STOCK sEcoNo/ 1P2 RECYCLE STOCK CHARGING STOCK l NVENTORCLARENCE G. GERHOLD Patented Feb. 10, 1942 rrr rice CONVERSION OF HYDROCApplication July 14, 1939, Serial No. 284,446

4 Claims.

The invention relates specifically to an improved process of crackinghydrocarbon oils to produce therefrom high yields of good antiknockgasoline and residual liquids of the desired characteristics.

One specific embodiment of the invention comprises cracking virginhydrocarbon oil charging stock for the process, separating the resultingconversion products into vapors and heavy liquid residue, fractionatingthe vapors to recover therefrom gasoline of low end-boiling point and tocondense their higher boiling components as reflux condensate,separately cracking said refiux condensate under independentlycontrolled more severe cracking conditions than those to which saidcharging oil is subjected, separating the resulting products into vaporsand a residual liquid substantially lighter than that separated from thefirst mentioned conversion products, fractionating the last named vaporsseparate from those aforementioned to recover therefrom gasoline ofsubstantially higher end-boiling point than that recovered from thefirst named vapors and to condense their higher boiling components asreflux condensate, supplying the last named reflux condensate to thefirst mentioned cracking-step for further cracking treatment therein incommingled state with the charging oil and commingling said lowend-point and high end-point gasolines to form the final, full boilingrange gasoline product of the Process.

The process herein provided has several advantages over conventionalselective cracking operations of the type in which virgin charging oiland reflux condensate or recycle stock recovered from vaporous productsof the raw oil cracking operation are separately cracked underindependently controlled conditions. The residual liquid fractionsnormally obtainable by the cracking of relatively heavy virgin oils,such as topped or reduced crude, fuel oil and the like, containsubstantial quantities of relatively lowboiling fractions which aresusceptible to further cracking to produce substantial additional yieldsof gasoline. In the present invention, the heavy residual liquidrecovered from the products of the cracking operation to which thecharging oil is supplied are substantially devoid of such desirablelight fractions, the latter being stripped therefrom by flashdistillation and included in the recycle stock supplied to the othercracking step of the system wherein they are converted into additionalyields of gasoline. A lighter liquid residue is recovered from theproducts of the second mentioned cracking step. Since the productsformed in this cracking operation are of a more highly aromatic naturethan those formed by cracking of the charging oil, the relatively lightcomponents of this residual productwould produce much smaller yields ofgasoline and higher yields of coke and gas upon further cracking andare, therefore, not desirable as components of the recycle stock.

Due to the less aromatic nature of the products resulting from crackingof the charging oil, as compared with those resulting from cracking therecycle stock recovered from the products of the cracking operation towhich the charging oil is supplied, the gasoline formed by cracking ofthe charging oil is of lower antiknock value than that formed byseparate cracking of said recycle stock and, in the present invention,to improve the antiknock value of the final gasoline product, relativelyheavy gasoline fractions of the products of the first mentioned crackingoperation are included in the recycle stock recovered therefrom andsupplied to the second mentioned cracking operation wherein they arefurther cracked or reformed to improve their antiknock value,fractionation of the vaporous products of the two cracking operationsbeing accomplished in separate zones and regulated to producefractionated vapors containing higher end-point gasoline from thevaporous products of the second mentioned cracking operation, ascompared with the gasoline included in the fractionated vapors of thefirst mentioned cracking operation, and the two gasoline products areblended to form the final full boiling range gasoline product of theprocess.

Reflux condensate or recycle stock condensed from the vaporous productsof the second mentioned cracking operation is of narrower boiling rangethan that condensed from the vaporous products of the first mentionedcracking step and by returning this material, as herein provided, to theinitial cracking step, wherein it is further cracked in commingled statewith the charging oil, a two-fold advantage is obtained. First, thematerial serves as a diluent for the heavier charging stock and permitsthe use of more severe cracking conditions in the initial cracking stepthan those to which the heavy charging stock alone could beadvantageously subjected, whereby the gasoline resulting from thiscracking operation is improved in antiknock value. Secondly, by thismethod of operation the conversion products of the initial cracking stepwill include a greater quantity of relatively low-boiling vapors. Thispermits more extensive flash distillation of these products, whereby toform the desired relatively heavy residual product and include in thevapors subjected to fractionation and in the reflux condensate orrecycle stock formed in this step relatively heavy fractions suitablefor further cracking, which desirable heavy fractions could not beseparated from the heavy residue by flash distillation if the heavycharging stock were cracked alone or in the absence of lighterfractions.

It will be apparent that the various features of the process, as aboveoutlined, are mutually cooperative and interdependent. Although nonovelty is claimed for any individual step of the process per se,invention is believed to reside in the novel and advantageous manner inwhich the various steps are herein cooperatively combined.

The accompanying drawing is essentially a How diagram of the processprovided by the invention and in conjunction with the followingdescription will serve to further illustrate the methd of operationcontemplated by the invention.

Referring to the drawing, the virgin hydrocarbon oil charging stock,which preferably comprises heavy crude oil, reduced or topped crude,fuel oil or the like, is supplied through line I and valve 2 to crackingzone 3 which may be any suitable form of cracking equipment, such as,for example, an externally heated cracking coil or a cracking coil andreaction chamber connected in series. The charging oil is cracked inZone 3 in commingled state with lighter hydrocarbon oil supplied to thiszone from Within the system, as will be later described, underconditions of temperature, pressure and time regulated to produce highyields of gasoline from the commingled oils. The resulting conversionproducts are directed through line 4 and valve 5 to separating andfractionating zone B.

Substantial superatmosph'eric pressure is employed in cracking zone 3and this pressure is substantially reduced in zone 5 to accomplishextensive further vaporization or flash distillation of the liquidcomponents of the conversion products supplied thereto. The vaporousconversion products, including those evolved by said flash distillation,are separated from the remain ing heavy non-vaporous residue in zone 6and the residual liquid is removed from the system to cooling andstorage or elsewhere, as desired, through line 'I and valve 8. Thevapors are fractionated in zone 6 to separate normally gaseouscomponents and gasoline fractions of relatively low end-boiling pointfrom their higher boiling components, which latter are condensed asreflux condensate or recycle stock for further cracking.

The low end-point gasoline vapors and gases are directed from zone 6through line 9 and valve In to condensing and separating equipment, aswill be later described, and the reflux condensate or recycle stockformed in zone 6 is directed therefrom through line I I and valve I?! topump l3 by means of which it is supplied through line H and valve I 5 tofurther cracking treatment in cracking zone IS.

The relatively wide boiling range recycle oil supplied to zone I6 issubjected therein to independently controlled cracking conditions,preferably more severe than those employed in zone 3. Zone It maycomprise any suitable form of cracking equipment and the conversionproducts formed therein are directed through line H and valve l3 toseparating and fractionating zone 19 which is preferably operated at asubstantially reduced pressure relative to that employed in zone 16 toeffect flash distillation and further vaporization of the liquidcomponents of the conversion products. However, less extensive flashdistillation is accomplished in zone NJ, as compared with thataccomplished in zone 6 and the non-vaporous liquid residue removed fromzone l9 through line 20 and valve 2| to cooling and storage orelsewhere, as desired, is of a lighter nature than that removed fromzone 6.

Thevaporous components of the conversion products supplied to zone 19and the vapors evolved by flash distillation therein are fractionated toseparate therefrom normally gaseous fractions and gasoline vapors ofhigher endboiling point than those removed from zone 6 and to condensetheir higher boiling fractions as reflux condensate or recycle stock.The latter is directed from zone 19 through line 22 and valve 23 to pump24 by means of which it is supplied through line 25 and valve 28 tofurther cracking treatment in zone 3 in commingled state with th virgincharging stock.

The gases and high end-point gasoline fractions, resulting from thefractionation afforded the vapors in zone l9, are directed therefromthrough line 21 and valve 28 and commingle in line 29 with the gases andlower end-point gaso line vapors from zone 8, the comrningled materialsbeing directed to condensing zone 30 wherein the are cooled sufiicientlyto condense substantially all of their normally liquid fractions. Theresulting distillate and uncondense'd gases are directed through line 3|and valve 32 to collection and separation in zone 33 wherefrom saiddistillate, which comprises the full boiling range gasoline product ofthe process, is directed through line 34 and valve 35 to storage or toany desired further treatment. The gases which remain uncondensed andundissolved in the distillate recovered from zone 33 are directedtherefrom through line 36 and valve 3'! to storage or elsewhere, asdesired.

The preferred range of operating conditions which may be employed inconducting the process of the invention are approximately as follows:The maximum temperature to which the charging stock is heated will varydepending upon its characteristics and may range, for example, from 800to 950 F., or thereabouts, preferably with a superatmospheric pressurein this cracking zone of the order of to 500 pounds, or more, per squareinch. The maximum temperature to which the first recycled stock isheated in cracking zone [6 may range, for example, from 850 to 1000 F.,or thereabouts, and preferably a superatmospheric pressure of the orderof to 800 pounds, or more, per square inch is employed in this zone.Separation of the products from each cracking zo'ne into vapors andnon-,vaporcus residue is accomplished at a substantially reducedpressure relative to that employed in the corresponding cracking zoneand the residual liquid resulting from cracking of the charging oil andsecond recycle stock is subjected to more extensive flash distillationthan that resulting from cracking of the first recycle stock, either byemploying lower pressure or higher temperature, or both, in theseparating zone to which the products of cracking zone 3 are supplied.The pressure employed in the fractionating, condensing and collectingportions of the system may be substantially the same or somewhat lowerthan that employed in the preceding flash distilling zone employing thelowest pressure or, when desired, fractionation of the vaporous productsof the two cracking steps may be accomplished at different pressures, inwhich case a pressure corresponding to or less than that employed in thefractionating zone utilizing the lowest pressure is employed in thecondensing and collecting equipment, when the overhead vaporous streamsfrom the two fractionating zones are commingled. It is, however, withinthe scope of the invention to separately condense the overheaddistillate product of each fractionating step and subsequently blend thelow end-point and high end-point gasolines produced in any desiredproportion.

As an example of one specific operation of the process, the chargingoil, which is a 25 A. P. I. gravity Mid-Continent topped crude, issubjected in zone 3, together with the recycle stock formed in zone l9to a cracking temperature of approximately 920 F. "at a superatmosphericpressure of about 200 pounds per square inch. The resulting vaporous andliquid conversion products are supplied to the vaporizing or flashdistilling section of zone 6 which is operated at a superatmosphericpressure of approximately 30 pounds per square inch. This pressure issubstantially equalized in the succeeding fractionating, condensing andcollecting equipment. The total reflux condensate formed in zone B issubjected in zone IE to a cracking temperature of approximately 960 F.at a superatmospheric pressure of about 350 pounds per square inch andthe products from this step are cooled to a temperature of approximately750 F. by commingling the sam with precooled regulated quantities of thereflux condensate formed in zone l9 and the commingled materials areintroduced into the vaporizing or flash distilling section of the latterzone which is operated at a superatmospheric pressure of approximately100 pounds per square inch. The fractionating section of zone I9 isoperated at substantially the same pressure and the pressure of theoverhead vaporous stream therefrom is reduced to approximately 30 poundsper square inch before being commingled with the overhead vaporousstream from zone 6.

The residual liquid recovered from the products resulting from crackingof the charging oil and second recycle stock has a, gravity ofapproximately 337 A. P. I., a viscosity of approximately 800 S. F. S. at122 F. and amounts to approximately 26% by volume of the charging 011.The residual liquid recovered from the products resulting from crackingof th first recycle stock has a gravity of approximately A. P. I., aviscosity of approximately 30 S. F. S. at 122 F. and amounts toapproximately 9% by volume of the charging oil. The end-boiling point ofthe gasoline recovered from the fractionating step of the initialcracking operation is approximately 250 F. and that recovered from thefractionated vapors of the cracking operation to which the first recyclestock is supplied has an endboiling point of approximately 400 F. Theblended gasoline product amounts to approximately 55% by volume of thecharging oil and has an octane number of approximately 70-72 asdetermined by the motor method.

I claim as my invention:

1. The process of cracking hydrocarbon 011s,

which comprises cracking a virgin residual oil charging stock undersufficient superatmospheric pressur to maintain a substantial portionthereof in liquid phase, separating the resulting products at asubstantially reduced pressure into vapors and heavy residual liquid andrecovering the latter, fractionating the vapors to separate therefromnormally gaseous fractions and ood antiknock gasoline of relatively lowend-boiling point and to condense their higher boiling components asreflux condensate, separately cracking said reflux condensate underconditions regulated to improve the antiknock value of the relativelyhigh-boiling gasoline fractions included therein and to convert itshigher boiling components into substantial additional yields of goodantiknock gasoline, separating the resulting vaporous and liquidproducts under a pressure substantially higher than said reducedpressure whereby to produce a substantially lighter residual liquid thanthat recovered from the products of the initial cracking step,'fractionating the last named vapors to separate therefrom normallygaseous fractions and gasoline of substantially higher end-boiling pointthan that included in the fractionated vapors of the initial crackingstep, subjecting the fractionated vapors of both cracking operations tocondensation to form said low end-point and said high endpointgasolines, and blending the latter 'in regulated proportions to form thefinal full boiling range gasoline product of the process.

,2. The process of cracking hydrocarbon oils, which comprises cracking avirgin residual oil charging stock under sufiicient superatmosphericpressure to maintain a substantial portion thereof in liquid phase,separating the resulting products at a substantially reduced pressureinto vapors and heavy residual liquid and recovering the latter,fractionating the vapors to separate therefrom normally gaseousfractions and good antiknock gasoline of relatively low end-boilingpoint and to condense their higher boiling components as refluxcondensate, separately cracking said reflux condensate under conditionsregulated to improve the antiknock value of the relatively high-boilinggasoline fractions included therein and to convert its higher boilingcomponents into substantial additional yields of good antiknockgasoline, separating the resulting vaporous and liquid products under apressure substantially higher than said reduced pressure whereby toproduce a substantially lighter residual liquid than that recovered fromthe products of the initial cracking step, fractionating the last namedvapors to separate therefrom normally gaseous fractions and gasoline ofsubstantially higher end-boiling point than that included in thefractionated vapors of the initial cracking step, and to condense theirhigher boiling fractions as reflux condensate, subjecting thefractionated vapors of both cracking operations to condensation to formsaid 10w end-point and said high end-point gasolines, blending thelatter in regulated proportions to form the final full boiling rangegasoline product of the process, and further cracking the 'lastmentioned reflux condensate in the initial cracking step with saidcharging stock.

3. The process of cracking hydrocarbon oils, which comprises cracking avirgin residual oil charging stock under sufiicient superatmosphericpressure to maintain a substantial portion-thereof in liquid phase,separating the resulting products at a substantially reduced pressureinto vapors and heavy residual liquid and recovering the latter,fractionating the vapors to separate therefrom normally gaseousfractions and good antiknock gasoline of relatively low end-boilingpoint and to condense their higher boiling components as refluxcondensate, separately cracking said reflux condensate under conditionsregulated to improve the antiknock value of the relatively high-boilinggasoline fractions included therein and to convert its higher boilingcomponents into substantial additional yields of good antiknockgasoline, separating the resulting vaporous and liquid products under apressure substantially higher than said reduced pressure whereby toproduce a substantially lighter residual liquid than that recovered fromthe products of the initial cracking step, fractionating the last namedvapors to separate therefrom normally gaseous fractions and gasoline ofsubstantially higher end-boiling point than that included in thefractionated vapors of the initial cracking step and to condense theirhigher boiling fractions as reflux condensate, and subjecting thefractionated vapors of both cracking steps to condensation in commingledstate to form the final full boiling range gasolin product of theprocess.

4. The process of cracking hydrocarbon oils, which comprises cracking avirgin residual oil charging stock under sufficient superatmosphericpressure to maintain a substantial portion thereof in liquid phase,separating the resulting products at a substantially reduced pressureinto vapors and heavy residual liquid and recovering the latter,fractionating the vapors to separate therefrom normally gaseousfractions and good antiknock gasoline of relatively low end-boilingpoint and to condense their higher boiling components as refluxcondensate, separately cracking said reflux condensate under conditionsregulated to improve the antiknock value of the relatively high-boilinggasoline fractions included therein and to convert its higher boilingcomponents into substantial additional yields of good antiknockgasoline, separating the resulting vaporous and liquid products under apressure substantially higher than said reduced pressure whereby toproduce a substantially lighter residual liquid than that recovered fromthe products of the initial cracking step, fractionating the last namedvapors to separate therefrom nor- .mally gaseous fractions and gasolineof substantially higher end-boiling point than that included in thefractionated vapors of the initial cracking step and to condense theirhigher boiling fractions as reflux condensate, subjecting thefractionated vapors of both cracking steps to condensation in commingledstate to form the final full boiling range gasoline product of theprocess and further cracking the last mentioned reflux condensate in theinitial cracking step with said charging stock.

CLARENCE G. GERHOLD.

